Generally, incremental or absolute encoding schemes can be used to measure the angular position of a rotating device, such as a volume-control knob or the crown of an electronic watch. In many applications, such rotating control elements are also axially displaceable in order to trigger or activate various functions of a device. Therefore, it may also be necessary to measure the axial position of the same knob or crown. In watch applications, the axial position of setting stem, which is usually terminated by a crown at its distal end, is used to change the modes of the watch, such as current time display, date setting, and time setting, for example. If the crown is pulled out one discrete axial position to enter the date setting mode, angular rotation of the crown is then used to move from one day to the next. If the crown is pulled out two discrete axial steps, angular rotation of the crown will then be used to set the time.
For determining or measuring axial and/or angular movements and/or positions of a rotational device, a sensor arrangement is generally needed to detect a coding pattern on the rotational device. It is desirable that such a sensor arrangement provide a high resolution angular and/or translational movement or position detection and that the wear in the sensor arrangement be minimised. Furthermore, it would be desirable to obtain a position or relative movement detection arrangement that is simple to assemble and takes up little space.